Transcript Cisco 3 Mod9 ppt[1].

Cisco Networking
Academy
Version 3.0
Module 9 VLAN Trunking
Protocol
George Karnbauer, CCNA
Trunking
Trunking
• A trunk is a
physical and
logical
connection
between two
switches across
which network
traffic travels.
Trunking Concepts
• A trunk may be a physical or logical
connection between devices.
• A trunk is a point-to-point link
capable of supporting multiple
VLAN’s.
• Trunking will bundle multiple virtual
links over one physical link by
allowing the traffic for several
VLAN’s to travel over a single cable
between the switches.
Trunking Operation
• Two main methods are used to
enable trunking:
– Cisco proprietary protocol, InterSwitch Link (ISL)
– IEEE 802.1q
• Both use frame-tagging to
identify multiple VLAN
information to pass on a single
trunk link.
IEEE 802.1q
• IEEE 802.1q is the open
standard Trunking protocol used
by most switches.
• Places a unique identifier in the
header to identify which VLAN a
frame is communicating on.
• The ID is removed when the
frame reaches it’s final switch
destination.
Inter-Switch Link (ISL)
• Cisco’s proprietary method of
frame-tagging.
• Encapsulates the Ethernet
frame with information that
contains the VLAN ID.
• Only used on Cisco devices.
Trunking
Implementation
• To implement Trunking, the
following steps must be taken:
– Configure port as a trunk port.
• Switch1(config-if) switchport mode
trunk
– Specify port encapsulation method
• Switch1(config-if) switchport trunk
encapsulation dot1q
– Verify trunking is enabled.
• Switch1# Show Trunk
VLAN Trunking ProtocolVTP
VTP
• VLAN Trunking Protocol (VTP)
was created to solve operational
problems in a switched network
with VLAN’s.
VTP
• VTP is a messaging protocol
that uses Layer 2 trunk frames
to manage the addition,
deletion, and renaming of
VLAN’s on a single domain.
VTP
• VTP allows for centralized
changes that are communicated
to all other switches in the
network.
• VTP messages are encapsulated
in either Cisco proprietary InterSwitch Link (ISL) or IEEE 802.1Q
protocol frames, and passed
across trunk links to other
devices.
Benefits of VTP
• VTP has the following benefits:
– Configuration consistency across
the network.
– Ability to trunk across mixed
media networks.
– Reduces complexity of managing
and monitoring VLAN’s across the
network.
VTP Trunks
• Switch ports can be assigned to
VLAN’s or as Trunk ports.
• To assign a switch port to a
VLAN;
– Switch1(config-if)switchport mode
access
• To assign a switch port as a
trunk port;
– Switch1(config-if)switchport mode
trunk
Switch Port Assignment
• While switch ports are normally
assigned to only one VLAN,
trunk ports, by default, carry
data from all VLAN’s.
VTP Operation
• A VTP domain is made up of one
or more interconnected devices
that share the same VTP domain
name.
• A switch can be in one VTP
domain only.
VTP Switch Modes
• A VTP switch can operate in one
of three modes:
– Server
– Client
– Transparent
VTP Server Mode
• VTP servers can create, modify, and
delete VLAN and VLAN configuration
parameters for the entire domain.
• VTP servers save VLAN configuration
information in the switch NVRAM.
• VTP servers send VTP messages out
to all trunk ports.
VTP Client Mode
• VTP clients cannot create,
modify, or delete VLAN
information.
• The only role of VTP clients is to
process VLAN changes and send
VTP messages out all trunk
ports.
VTP Transparent Mode
• Switches in VTP transparent
mode forward VTP
advertisements but ignore
information contained in the
message.
VTP Transparent Mode
• A transparent switch will not
modify its database when
updates are received, nor will
the switch send out an update
indicating a change in its VLAN
status
• Except for forwarding VTP
advertisements, VTP is disabled
on a transparent switch.
VLAN Implementations
• A switch will advertise its:
– Management Domain
– Revision Number
– VLAN’s it knows about
• In small networks, most
switches will be set as servers.
• Each switch will send this
information every five minutes
VLAN Implementations
• VTP Advertisements are sent via
multicast.
• Each has a revision number
assigned.
• When a switch sends an
advertisement with new
information, it increases the
revision number by 1. (N+1)
VTP Advertisements
• Types of VTP advertisements:
• Advertisement requests
• Summary advertisements
• Subset advertisements
Advertisement Requests
• When a new device is booted, an
advertisement request is
generated.
• A server will then respond with
a summary advertisement or a
subset advertisement.
Summary Advertisement
• Sent every five minutes.
• List current revision number.
• If revision is same as client, it
stops.
• If revision number is higher,
client requests subset
advertisement.
Subset Advertisement
• Subset advertisements contain
detailed information about
VLAN’s such as VTP version
type, domain name and related
fields, and the configuration
revision number.
Subset Advertisement
• The following trigger these
advertisements:
–
–
–
–
Creating or deleting a VLAN
Suspending or activating a VLAN
Changing the name of a VLAN
Changing the maximum
transmission unit (MTU) of a VLAN
• A newly created VLAN will not
be advertised until ports are
assigned to it.
• VTP Configuration
VTP Configuration
• To configure VTP the following
must be done:
– Determine the VTP domain name,
Devices on different VTP domains
do not communicate VTP
information
– Determine VTP Version 1 or 2, 1 is
default
– Choose VTP mode of operation
VTP Configuration
• To change the VTP version issue
the following command:
– Switch1#Vlan database
– Switch1(VLAN)#vtp v2-mode
• For the first switch configured,
setup the VTP domain name:
– Switch1(VLAN)#VTP Domain
(Name)
VTP Configuration
• To setup switch as VTP Server:
– Switch1(VLAN)# vtp server
• When adding a new switch to a
VTP domain, first check the
existing revision number. Make
sure new switch has a lower
revision number.
– Switch1#Show vtp status
Inter VLAN
Communications
• Hosts on one VLAN can only
communicate directly with other
devices on the same VLAN.
• All devices on a VLAN should be part
of the same IP subnet.
• If a host on one VLAN wants to
communicate to a host on another
VLAN, it must go through a router.
Inter VLAN
Communications
• It is possible to
have a physical
connection for
each configured
VLAN.
• This topology
does not scale
well.
• This topology
wastes
connections.
Inter VLAN
Communications
• Using sub
interfaces and a
trunked link
allow multiple
VLAN’s to run on
a single link,
reducing the
number of ports
and wire runs
required.
Sub-Interface
Configuration
• To define sub-interfaces on a
physical interface, perform the
following tasks:
– Identify the interface.
– Define the VLAN encapsulation.
– Assign an IP address to the
interface
Sub-Interface
Configuration
Sub-Interface
Configuration
• When configuring subinterfaces, the interface address
must be a part of the subnet
assigned to the VLAN.
VTP Troubleshooting
• Switches can only be assigned
to one management domain.
• Sub-interfaces must be part of
the IP subnet assigned.
• VTP version numbers must be
the same for all switches in a
VTP domain.
VTP Troubleshooting
• When new switches are brought
into a Management domain, the
revision number must be lower
the current revision number.